Direct-current machine



A. SCHERBlUS.

DIRECT CURRENT MACHINE. APPLICATION FILED NOV. 25, 1914. RENEWED FEB. 4. 1920.

J Patented Sept. 14, 1920.

4 SHEETS-SHEET 1- A. SCHERBJUS. DIRECT CURRENT MACHINE.

APPLICATION HLED NOV. 25,1914- RENEWED FEB. 4. 1920.

1,352,920. fly j PatentedSept. 14,1920.

SHEETS--SHEET 2.

A. SCHERBIUS.

DIRECT CURRENT MACHINE.

APPLICATION FILED NOV-25,1914. azgiweo FEB. 4, 1-920.

1,352,920, PatentedSept. 14, 1920.

4 4 SHEETS-SHEET 3- jly5 f4 .9;

A. SCHERBIUS. DIRECT CURRENT MACHINE.

APPLICATION FILED NOV.25, 1914. RENEWED FEB. 4, 1920.

1,352,920, Patented Sept. 14, 1920.

4 SHEETS-SHEET 4- ARTHUR SCHERBIUS, OF BERLIN, GERMANY.

DIRECT-CURRENT MACHINE.

Specification of Letters Patent.

Patented Sept. 14, 132%.

Application filed November 25. 1914. Serial No. 874,061. Renewed February 4, 1820. Serial No. 356,125.

To all whom it may concern:

Be it known that I, ARTHUR SoHERniUs, a subject of the German Emperor, residing at Berlin, Charlottenburg 9, Germany, have invented certain new and useful Improvements in Direct-Current Machines, of which the following is a full and clear specification.

Commutation plays an important part in the proper operation of direct current machines.

As the brush slides over the commutato segments, the current in the coils connected .with the segments, which had a certain direction before the connection of the segments by the brush, must flow in the opposite direction after the brush has passed.

As is generally known, this commutation process is improved by letting the coils during the short circuit-ing by the brush rotate past auxiliary fields which produce a rotation tension in the coils, which causes the currents reversal. These fields must be made of ust the right size to insure that the current flowing from the segments to the brush passes through the zero point as exactly as possible at the moment the brush is leaving the corresponding segment. If the current has either not yet become zero, or ias already commenced flowing in the opposite direction a spark occurs as the brush leaves.

The object or the present invention is to avoid the formation of sparks at the commutator, even if the commutating field is not of the exact magnitude necessary.

The invention is illustrated in the accompanying drawing, in which Figures 1 to t show assembled diagrammatic views of the armature winding, commutators and check valve devices for controlling the commutated current.

Figs. 5 to 7 serve to illustrate the opera tions more in detail.

Fig. 8 represents a particular commutating device.

Figs. 9 and 10 represent particular modifications of the form shown in Figs. 8 and 5 respectively.

In Figs. 1 to 4: a direct current motor is shown, of which p are its field poles and a its armature winding. The armature winding is coupled with two commutators 7c, and i17 which have conducting segments spaced apart by the broad insulation pieces (Z. The

individual parts or the armature winding are each connected at their ends to the different segments of both commutators as shown in the drawing. The brushes 5,. b b 5,, are narrower than the insulation piece d, so that none of the brushes can short circuit two sections of the same commutator. The short circuit of an armature winding can only occur in common over the two brushes and their connecting conductors, and the brushes are located so relatively to the field poles that a suitable commutating field is produced and proper commutation occurs.

In these connecting conductors are arranged rectifiers (for example mercury vapor rectifiers) which in known manner possess the property of letting through electric current only in one direction while preventing the passage of current in the other direction.

The combining of such electrical check valves, which are arranged in the manner of rectifiers, with the above described form of commutator, forms the basis of the invention. These check valves in the present use do not have the purpose of rectifying the current, but have the sole purpose of improving the commutation and thus, while to be sure, they have certain physical properties in common with check valves em ployed as rectifiers, the employment of these properties is different.

The commutating process can be seen from .Figs. 1 to 4, which show a machine in the different commutating stages. The valves in which the current is flowing are shown shaded. As will be seen in Fig. 1, the current flows only in the valves o, and Q1 and in the brushes 6,, and 7),, while the brushes 5,, and b, and valves 12,, '0 are without cur rent. hen the armature turns as indicated by the arrow, the position indicated in Fig.

is directed against the current 2' previously flowing in the armature portion h. It thus has a tendency to neutralize the current in the valves 11,, and a, in order to drive it through the valves 1),, and 11 At the end of this period, the current 2' in the valves 0 and 0 drops to zero and is completely transferred to the valves v and 2),. After the current i has become Zero no more current can fiow as the valves are check valves. While the commutator tension 6 operates,

the armature moves from the: position shown currents in the gas contacts 0 and 0, are

interrupted.

Slight differences of tension at the advance edges of the brush are in general of less danger than the presence of a current where the brush is leaving. Greater difference in potential even at the forward edge can, however, be injurious to the commutator under bad commutating conditions. In order to. fully avoid sparkingalso on the forward edge, the commutation must be so arranged that before the projection of a brush upon a segment, a tension is produced in the armature winding connected with this segment, which will create a current against the valve operation, so that the flowing of a current, that is, the passage of a spark, to the projecting edge is avoided.

This relation may now be observed in more detail with relation to Figs. 5 and 7.

Figs. 5 to 7 show sections of the commutater and the winding of a motor (according to Figs. 1 to 4t) and especially that part which operates in the vicinity of the positive brush. The poles marked S and 'W constitute commutating fields.

The negative brushes are omitted for the sake of 'clearness.

The brush Z), in Fig. 5 is just at the point of passing on to the segment Z,. If a strong cornmutating electromotive force is already present in the armature coil, this might pro-. duce a spark between 6,, and 1,, and cause a high specific current load in the narrow projecting edge. In order to avoid this, a

tensionin the direction of the brush Z), isv produced in the armaturewinding to before the projection of the edge of brush Z), over Z,. This tension has the tendency of producing in theconductor g, a current in the direction of the arrowgo On account of ampere turns.

to 1),, as shown in Figs. 6 and 7 Inthe armature'position'of Fig. 6, the current flows inboth conductors g and 9 whereas in Fig. 7 it has already ceased in the conductOI g Fig. 8 shows an embodiment of an auxiliary pole arrangement by the aid of which commutation can be carried out in simple manner, as required according to the above explained theory.

In Fig. 8, h is an auxiliary pole which carries the commutatlng wlnding b. I This is so strong that it compensates the ampere turns of the armature in known manner and produces beyond this a field for commutation.

In order to avoid the occurrence of a ten- 7 sion at the brushes as they leave the segments, the auxiliary pole is provided with'a recess 02 in which a second winding 0 is disposed. .This has the purposeot' weakening the forward auxlhary field and strengthening the rear field. The winding 0 can be weak with respect to b as the electromagnetic forces which form the real auiriliary pole field are small as compared with the total ampere turns exciting the armature As the current of the winding 0 must change in direction with the direction of'rotation of the motor, it is desirable to connect these in series with the field winding, in case the motor is reversed by reversing the field. This is shown in Fig. 9, in which 79- represents the field poles having the field windings rv w h h are the auxiliary poles, carrying the comnrutat ing windings e -2 and also the windings c c respectively. In this figure the motor has shunt excitation, which is connected to the main by way of change-over switch uand rheostat 1". The switch serves for reversing the fieldwhereas the rlteostat serves for controlling same. The shunt exciting current flows from pole to 4 pole successively through four coils, m 0,, 0,, 00 The main circuit is independent thereof and flows from pole, .2 2-,, e "0 K b,,arn1ature, b b v v pole. Thus if the di-' rection of rotation is reversed by throwing switch u into the other position, the main cur rent flows in the same directionin the valves, brushes, armature and in the commutating windings 2,e of the auxiliary. poles, whereas in the exciting coils and in the small auxiliary coils 0,c, it is reversed. If the motor runs in but one direction then it is sufficient to provide a single piece auxiliary pole which corresponds in size and position with the left hand half of the auxiliary pole shown in Fig. 5. The right hand part can, in this case, be omitted. This is shown in F ig. 10. In this case a series motor connection is shown. Only the main current passes through the auxiliary windings in the following sequence: pole field coils 00 00 auxiliary coils e 2 valves '0 o,- brushes b ,b armature, brushes b b,, valves 41 -22 pole.

As distinguished from the use of an ordinary commutator, the connections have important advantages, as will be seen. One can construct the commutator with a smaller number of segments than is possible in the ordinary commutator, which is obvious from the following explanation.

One can produce a certain maximum. ten sion between two segments of the ordinary commutator. The limits of the tension are on the one hand determined by that tension which can not possibly pass the insulation, and on the other hand they are determined by the limit of tension up to which one can still commutate without sparks. As with the ordinary commutation means one can only compensate a definite percentage of the reaction tension occurring in the commutation,

the commutation will naturally become more difficult as the magnitude of the reaction tension between two segments becomes greater. It is, therefore, not directly possible with an ordinary commutator to increase the tension between two segments by increasing the insulation material as much as desired, because even if the increased layer of insulation resists the open spark tension, still the objectionable tension whichcan not be neutralized by exact commutation devices becomes so considerable that the commutator is destroyed. Therefore, if the actual commutation process is entirely removed from the commutator. so that the interruption of current or a closing of the current in the same never occurs and so that the same only opens or closes contacts which are without current or tension, one can increase the tension between two brushes per cm. of commutator surface, further than is possible in the ordinary commutator. One can also have fewer segments, because between two segments as high a tension as desired can be produced, if one makes the intervening insulation layer sufiiciently thick. As one is less limited in the breadth of the segments, the breadth of the brushes can also be increased and as much current can be taken from a commutator as is permissible with respect to its cooling outer surface. Especially are high tension commutators reduced in size over the previous forms, in this way.

It is obvious to anyone skilled in the art commutation irrespectively of the particular nature of such means.

I claim:

1. A direct current dynamo electric machine, comprising in combination an armature having a closed winding, two commutators havin electricall r conductive segments L 1 a I u n I alternatin with insulation )ieces and con nected alternately to the individual ends of the armature winding, a pair of brushes operating on each commutator, narrower than said insulation pieces, connections between the two brushes of a single pole, means for producing a commutating field, sharply defined in the directionof the armature conductors which first enter the commutating field, for over-cominutating the current in the armature coils which are shortcircuited by the brushes, and means for preventing current from flowing in a direction opposite to that in which the normal commutating current flows through said connections.

2. A direct current dynamo electric machine, comprising in combination an armature having a closed winding, two 001111111"; tators having electrically conductive segments alternating with insulation pieces and connected alternately to the individual ends of the armature winding, a pair f l rushes operating on each commutator, narrower than sail insulation pieces, connections between the two brushes of a single pole, means for producing a cominutating field sharply defined in the direction of the armature conductors which first .enter the coinnlutating field, for over-commutating the current in the armature coils which are short-circuited by the brushes and electric check valves inserted in said connections for preventing current from flowing in a direction opposite to that in which the normal commutating current flows through said connections.

3. A direct current dynamo electric niachine-comprising in combination an armature having a closed winding, an auxiliary field pole with two teeth having a winding between said teeth, two commutators having electrically conductive segments alternately connected to the individual ends of the closed armature winding, insulation pieces between said segments, brushes operating on said commutator and narrower than said insulation pieces, said auxiliary field pole producing over-commutation of the current in the armature coils short-cin cuited by the brushes, connecting conductors between the two brushes of a single pole, and electrical check valves inserted in said conductors for preventing current from flowing in a direction opposite to that in which, the normal commutating current flows through said conductors.

4. A direct current dynamo electric machine, comprising in combination an armature having a closed winding, an excitation field winding, an auxiliary field pole with two teeth having a winding between said teeth, connected in series with said excitation winding, two commutators having electrically conductive segments alternately connected to the individual ends of the closed armature winding, insulation pieces between said segments, brushes operating on said commutators and narrower than said insulation pieces,rsaid auxiliary field pole producing over-commutation of the current in the armature coils short-circuited by the brushes, connecting conductors betweenthe two brushes ofa single pole, and electrical check valves inserted in said conductors for preventing current from flowing in a direction opposite to that inwhich the normal commutating current flows through said conductors. I g p 5 ARTHUR SCHERBIUS,

Witnesses: i

HENRY HAsPER, VVOLDEMAR HAUPT. 

